This invention relates generally to the field of robotics and more particularly to a new and improved means for positioning a tool in space from one point to another. The tool may be one that attaches itself to an article or a tool to be moved. Historically, such devices are generally well known and before digital and analog computers many specific mechanisms have been designed and used for this purpose.
An example of a mechanism designed for positioning something from one place to another is a Means for Transferring Glassware, U.S. Pat. No. 1,771,641 by T. F. Lamb. Therein, jaws grab a milk bottle and swing it around a vertical axis to another position based on the swing of a frame holding the milk bottle until it is at a new position based on the arc travelled by the jaws and frame. The operation of the jaws for grabbing and releasing the milk bottle and the rotating frame for moving the bottle around a radius over an arcuate distance is complicated and not readily adapted to more complex paths because the total design anticipates a single and specific path and no variations. Moreover, in the case of the above identified patent, the path is all at one elevation. The major limitations besides inflexibility appear to be the complexity and lack of adaptability to a wide range of uses.
More complex requirements exist such as those conditions that occur when an article such as a bottle is to be moved over a path which does not fit nicely on the arc to be travelled by the rotating frame and jaws. When a more complex path of travel is added, the mechanical problems increase tremendously. Suppose the path to be travelled also includes a requirement that the article be raised or lowered as well as moved on an arc at a fixed radius at the same elevation. One way to accomplish this requirement is illustrated by a patent entitled: Bunch Transfer for Cigar Machines, U.S. Pat. No. 1,740,575. In this example, the cigars are gripped and a transfer arm moves around its pivot point over an arcuate distance over the top in a vertical loop with a fixed radius, and the cigars are moved to a different point on the arcuate path, but at a different elevation or at the same elevation. Here again, the path of the cigars, mechanically set by the apparatus and the equipment, is a specific solution to a specific problem. Also, generally it is not susceptible to variation nor capable of adapting itself to control techniques made available through the enormous change brought about in both analog and digital computer technology.
With the advent the new technology for mechanical positioning or transferring articles now generally referred to as robotics, those skilled in the art can make systems electrical mechanical that move a holder of a tool or an article from any point in space to another point in space using three axis positional control mechanisms for translation, with greater flexibility or adaptability of the equipment to move the holder and/or article over any selected path. Digital technology has played a major role in this type of equipment because selected computer programs with appropriate input can change the path of movement of the tool as desired. However, in those cases, the electro-mechanical systems as well as the computer program become quite complex. Moreover, those skilled in the art recognize that accepted constraints in the path for the tool or tool holder can well result in some simplification.
When a path in space is defined from one point to another, each point along the path, including the beginning and the end points, may be defined mathematically in two ways. First, X, Y, and Z coordinates may be defined from reference axes for each point on the path or polar coordinates may be defined for each point, two angles and a distance from the same axis.
The present invention resulted when the inventor recognized that an optimum compromise and acceptable constraints resulted from utilizing polar coordinate terms for each point along the path of a tool holder (or driven arm member) when the tool holder (or driven member) is maintained at a fixed distance from the polar axes of rotation. Also, he recognized that where all three (the two polar angles and the fixed distance from the two axes of rotation) define the points in space through which the tool or tool holder is to be moved, he could use electro-mechanical technology to control one of the polar angles and mechanical technology to control the other polar angle.
Furthermore, the teachings of the present invention accept some constraints on the two polar angles. For example, the polar angle which would correspond to the vertical axis is often not required to be greater than 360.degree.. The other polar angle which would correspond to the horizontal axis is, for simplicity purposes, offset a small or minimum distance from the vertical axis. Although, the invention would work substantially the same way where there is no offset, the offset simplifies the mechanical pivot construction for the holder arm. As stated above, the major constraint is that the length of the holder arm (driven arm) determines the distance of the working end of the holder (or driven arm), as a point in space about both the vertical and horizontal axes at all times. This is an acceptable constraint in a large percentage of industrial applications.